Device for releasing a pair of conveying members and image forming apparatus including the same

ABSTRACT

A releasing device of the present invention selectively moves one of a pair of conveying members for conveying a sheet into or out of contact with the other conveying member. A first moving device moves the one conveying member into or out of contact with the other conveying member. A second moving device  72 is connected to the first moving device for moving the one conveying member in a releasing direction independently of the operation of the first moving means.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a releasing device for releasing a pair of conveying members configured to convey a sheet while nipping it therebetween and an image forming apparatus including the same.

2. Description of the Background Art

It is a common practice with a printer, copier or similar image forming apparatus to convey a sheet with a pair of conveying members. When a sheet jam or similar conveyance error occurs on a sheet path arranged in such an image forming apparatus, the operator of the apparatus usually stops the operation of the apparatus, locates the sheet jam and then removes a jamming sheet by hand. However, if the apparatus stops operating with the conveying members held in contact with each other, then a sheet nipped between the conveying members cannot be easily removed and, moreover, it is apt to be conveyed deeper into the apparatus by the conveying members after the sheet jam. This makes jam processing extremely troublesome.

In light of the above, Japanese Patent Laid-Open Publication No. 7-237782(=U.S. Pat. No. 5,544,580) proposes a system applied to a pair of feed rollers one of which is selectively movable toward or away from the other and conveying, when moved toward the other feed roller, a sheet by nipping it and including preventing means for preventing, when a conveyance error is sensed on a sheet path, the one feed roller from being moved toward the other feed roller. The preventing means includes a cam for causing an arm to move in a contacting/releasing direction, a stop protruding into the locus of angular movement of the arm member for stopping the arm member, and drive means for moving the stop. When a conveyance error occurs, the drive means is energized to prevent the arm member from moving in the contacting direction. The cam is rotated to cause the arm member to angularly move for thereby moving one of the two feed rollers into or out of contact with the other feed roller.

The conventional system described above has the following problem left unsolved. Assume that the drive means assigned to the arm member is energized due to a sheet jam or similar conveyance error occurred when the two feed rollers are held in contact with each other. Then, the arm member prevents the stop from smoothly protruding into the locus of angular movement of the arm member. Stated another way, the stop cannot function at all unless the cam holds the arm member in the releasing position. Therefore, even if the drive means assigned to the stop is energized as soon as, e.g., a sheet jam is sensed, the feed rollers, contacting each other, cannot be released immediately in dependence on the position of the arm member. As a result, the feed rollers convey a sheet and aggravate the sheet jam condition, rendering recovery work extremely troublesome.

Technologies relating to the present invention are also disclosed in Japanese Patent Laid-Open Publication No. 6-1492.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a releasing device promoting easy removal of a jamming sheet and an image forming apparatus including the same.

A releasing device of the present invention selectively moves one of a pair of conveying members for conveying a sheet into or out of contact with the other conveying member. A first moving device moves the one conveying member into or out of contact with the other conveying member. A second moving device 72 is connected to the first moving device for moving the one conveying member in a releasing direction independently of the operation of the first moving means.

An image forming apparatus including the above releasing means is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:

FIG. 1 is a front view showing the general construction of an image forming apparatus embodying the present invention;

FIG. 2 is a plan view showing a releasing device included in the illustrative embodiment;

FIG. 3 is an enlarged section showing the releasing device;

FIG. 4 is an enlarged section demonstrating how the releasing device releases a conveying member;

FIG. 5 is an enlarged section showing the operation of second moving means included in the releasing device;

FIG. 6 is a schematic block diagram showing a control system included in the illustrative embodiment;

FIG. 7 is a plan view showing a modification of the illustrative embodiment; and

FIG. 8 is a block diagram showing a control system included in the modification of the illustrative embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, an image forming apparatus embodying the present invention is shown and implemented as a stencil printer by way of example. As shown, the stencil printer, belonging to a family of printers, includes a printer body or apparatus body 1 accommodating a sheet feeding section 3, a printing section or image transferring section 4, and a sheet discharging section 6. The sheet feed section 3 feeds sheets 2 stacked thereon one by one while the printing section 4 prints an image on the sheet 2 fed from the sheet feed section 3. The sheet discharging section 6 discharges the sheet, or print, 2 coming out of the printing section 4 to the outside of the printer body 1. The stencil printer further includes a releasing device 70 and a control unit or control means 50 for controlling the entire stencil printer.

An image scanner or image reading section 40 is mounted on the top of the printer body 1 and has a conventional construction including a scanning unit 41A and a CCD (Charge Coupled device) image sensor or similar image sensor 41B. While the scanning unit 41A reads a document image, image data scanned by the scanning unit 31A are input to the image sensor 41B.

Mores specifically, the sheet feeding section 3 includes a sheet tray 10 loaded with a stack of sheets 2. Feed rollers 11 cooperated to pay out the top sheet 2 from the sheet tray 10 toward a registration roller pair or conveying member pair 12 while separating the underlying sheets from the top sheet. The registration roller pair 12 once stops the sheet to correct skew thereof and then conveys it toward the printing section 4 at preselected timing.

A sheet path 26 extends from the feed rollers 11 to the printing section 4. The registration roller pair 12 is made up of a drive roller or elastic member 12A formed of rubber and facing the sheet path 26 from below the same and a driven roller 12B formed of resin and facing the sheet path 26 from above the same. The driven roller 12B is held in contact with the drive roller 12A in such a manner as to be releasable from the latter, as will be described specifically later. The driven roller 12B may be formed of metal, if desired.

A stepping motor or drive motor 28 causes the drive roller 12A to rotate. The driven roller 12B, contacting the circumference of the drive roller 12A, is caused to rotate by the drive roller 12A. A jam sensor or conveyance error sensing means 27 is positioned on part of the sheet path extending between the registration roller pair 12 and the printing section 4. The jam sensor 27 is configured to output a jam signal on sensing a sheet jam, which is a specific conveyance error.

A master making section 7 is located at the upper right of the printing section 4 and includes a stencil storing section 14 in which a stencil 13 is stored in the form of a roll. A thermal head 15 and a platen roller or platen conveying member 16 are held in contact with each other at a positioned downstream of the master storing section 14 in a direction in which the stencil 13, paid out from the roll, is conveyed. Let this direction be referred to as a direction of stencil conveyance hereinafter. A cutter or cutting means 17 and a roller pair or stencil conveying member pair 18 are arranged downstream of the thermal head 15 and platen roller 16 in the direction of stencil conveyance. With this configuration, the master making section 7 perforates, or cuts, the stencil 13 in accordance with image data to thereby produce a master 19 and conveys the master 19 toward the printing section 4.

The printing section 4 is formed between a print drum 20 and a press roller or pressing member 22. The print drum 20 is a porous, hollow cylindrical body configured such that the master 19 produced by the master making section 7 is to be wrapped around its outer periphery 20 a. The press roller 22 is selectively moved into or out of contact with the outer periphery 20 aof the drum 20 by a mechanism, not shown, and presses, when moved into contact with the periphery 20 a, the sheet 2 against the periphery 20 a. The press roller 22, serving as a pressing member, may be replaced with a conventional print drum, if desired.

Ink feeding means 9 is arranged within the print drum 20 and made up of an ink conveying member 21 and a doctor conveying member 8. When the press roller 22 presses the sheet 2 fed from the sheet feeding section 3 against the master 19 wrapped around the drum 20, ink fed from the ink feeding means 9 is transferred to the sheet 2 via the print drum 20, forming an image on the sheet 2. A sheet discharging device is arranged at the upper left of the print drum 20 in order to peel off the used master 19 from the drum 20 and discard it, although not shown specifically. The print drum 20 is caused to rotate clockwise, as viewed in FIG. 1, by a main motor 29.

In the illustrative embodiment, the print drum 20 and registration roller pair 12 each are driven by a respective motor. Alternatively, the main motor 29 and drive roller 12A may be operatively connected to each other by any conventional drive transmission mechanism including, e.g., gears or pulleys so as to interlock the print drum 20 and registration roller pair 12.

The sheet discharging section 6 includes a peeler 23 for peeling off the sheet 2 adhering to the master 19 on the print drum 20 due to the viscosity of ink. A belt conveyor 25 conveys the sheet 2 coming out of the printing section 4 while sucking it with a suction fan 24. Such sheets or prints, sequentially driven out of the printer body 1, are sequentially stacked on a print tray 35.

As shown in FIGS. 2 and 3, the releasing device 70 includes first moving means 71 and second moving means 72. The first moving means 71 is configured to selectively move the driven roller 12B into or out of contact with the drive roller 12A. The second moving means 72 is connected to the first moving means 71 in such a manner as to move the driven roller 12B away from the first roller 12A (spacing direction hereinafter) independently of the operation of the first moving means 71.

More specifically, the first moving means 72 includes a pair of arms or angularly movable members 73A and 73B supporting the driven roller 12B and moving it into or out of contact with the drive roller 12A. A pair of coiled tension springs or biasing members 74A and 74B cooperate to constantly bias the arms 73A and 73B toward the drive roller 12A. A cam member 75 is rotatably connected to the arm 73A and rotatable to move the arms 73A and 73B in a contacting/spacing direction.

As shown in FIG. 2 specifically, a shaft 76 extends in a direction Y perpendicular to a direction of sheet conveyance X, as seen in a plan view. The direction Y corresponds to the widthwise direction of a sheet and will be referred to as a widthwise direction Y hereinafter. The driven roller 12B is 15 implemented as a plurality of rollers rotatably mounted on the shaft 76 at preselected intervals. Likewise, the drive roller 12A is implemented as a plurality of rollers rotatably mounted on a shaft 77, which also extends in the widthwise direction Y, at preselected intervals and each facing one of the driven 20 rollers 12B. A stepping motor 28 is drivably connected to the shaft or drive shaft 77 via a drive transmission mechanism not shown.

Opposite ends of the shaft 76 are affixed to one end 73 aof the arms 73A and 73B. The other ends 73 bof the arms 73A 25 and 73B are affixed to a rotatable shaft 78 journalled to the printer body 1, FIG. 1, so that the arms 73A and 73B can move the driven roller 12B toward or away from the drive roller 12A. The tension springs 74A and 74B are respectively retained by the arm members .73A and 73B at one end and retained by hooks 79 included in the printer body 1, FIG. 1, at the other end, constantly pressing the circumferential surface of the driven roller 12B against that of the drive roller 12 a.

A cam follower arm 81 is affixed to the end 78 aof the rotatable shaft 78 at one end 81 band therefore angularly movable in interlocked relation to the arm members 73A and 73B. A roller 80 is rotatably mounted on the other or free end 81 aof the cam follower arm 81. The cam member 75 is operatively connected to a drive transmission mechanism, not shown, in such a manner as to rotate about a shaft 82 in synchronism with the rotation of the print drum 20 when the main motor 29 is energized. In the illustrative embodiment, the can member 78 is configured to make a single rotation in synchronism with a single rotation of the print drum 20.

The cam member 75 has a circumferential cam surface 75 afacing the roller 80 of the cam follower arm 81. The roller 80 is constantly pressed against the cam surface 75 aby the force of the tension springs 74A and 74B. The cam surface 75 aof the cam member 75 has a profile configured to maintain the driven roller 12B in contact with the drive roller 12A, as shown in FIG. 3, until the sheet 2 driven by the registration roller pair 12 has been nipped between the print drum 20 and the press roller 22, move the driven roller 12B away from the drive roller 12A, as shown in FIG. 4, when the leading edge of the sheet 2 is nipped between the print drum 20 and the press roller 22, and again bring the driven roller 12B to the position of FIG. 3 for conveying the next sheet 2. The driven roller 12B is pressed against the drive roller 12A by the tension springs 74A and 74B when held in the contact position shown in FIG. 3.

The second moving means 72 includes a pin 85 studded on the rotatable shaft 78. A link member 86 is connected to the arm members 73A and 73B at one end 86 athereof via the pin 85 and shaft 78. A release motor 87 is drivably connected to the other end 86 bof the link member 86 in order to move the link member 86 in a direction in which the arm members 73A and 73B move the driven roller 12B away from the drive roller 12A. This direction will be referred to as a releasing direction hereinafter.

A slot 89 is formed in one end portion 86 aof the link member 86 and extends in the releasing direction mentioned above. The pin 85, studded on the shaft 78, is loosely fitted in the slot 89. This configuration prevents the link member 86 from being displaced when the arm members 73A and 73B are angularly moved by the cam member 75.

A worm gear 88 is mounted on the output shaft of the release motor 87, which is implemented as a stepping motor or a DC motor, and held in mesh with a gear portion 90 formed at the other end 86 bof the link member 86. In this condition, when the release motor 87 is driven to rotate the worm gear 88 clockwise, as viewed in FIG. 3, the worm gear 88 causes the link member 86 to move rightward, i.e., in the releasing direction.

FIG. 6 is a schematic block diagram showing a control system included in the illustrative embodiment. As shown, the control system includes the control unit 50 mentioned previously and constituted by a conventional computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory) and a timer. Connected to the output side of the control unit 50 are a sheet-feed drive section 42 for driving the sheet feeding section 3 including the stepping motor 18, a scanner drive section 43 including a drive source for driving the entire scanner 40 inclusive of the main motor 29, a master-make drive section 44 including a drive source assigned to the entire master making section 7, a print drive section 45 including a drive source for driving the entire printing section 4, a sheet-discharge drive section 46 including a drive section for driving the belt conveyor 25, and the release motor 87.

The jam sensor 27 and image scanner 40 and a control panel 60 are connected to the input side of the control unit 50. The control panel 50 includes a release key switch or release commanding means 61 for outputting a release command signal and a return key switch or return commanding means 62 for outputting a return command signal. The operator of the printer may operate the release key switch 61 when desiring to release the driven roller 12B from the drive roller 12A or operate the return key switch 62 after the removal of a jamming sheet or when desiring to return the driven roller 12B to the contact position.

Controlling the various drive sections of the printer, as needed, the control unit 50 controls the entire printing operation of the printer body 1. Further, when a jam signal is input to the control unit 50 from the jam sensor 27, the control unit 50 drives the release motor 87 in a direction that causes the link member 86 to move in the releasing direction, while interrupting the operation of the other devices. Also, when a release command signal is input to the control unit 50 from the release key switch 61, the control unit 50 drives the release motor 87 in the above direction. When the operator operates the return key switch 61, the control unit 50 drives, in response to the resulting return command signal, the release motor 87 in the opposite direction that causes the link member 86 to return to its initial position.

The operation of the illustrative embodiment will be described hereinafter. Assume that the master 19 is wrapped around the circumferential surface 20 aof the print drum 20 beforehand.

When the operator of the printer inputs a desired number of prints on ten keys, not shown, arranged on the control panel 60 and then operates a conventional print start key, the control unit 50 causes the sheet-feed drive section 42 to rotate the feed rollers 11 for thereby feeding the top sheet 2 from the sheet tray 10. Further, the control unit 50 causes the print drive section 45 to rotate the print drum 20 at a peripheral speed matching a preselected print speed. At this instant, although the driven roller 12B is held in contact with the drive roller 12A, as shown in FIG. 3, the stepping motor 28 is not driven, so that the leading edge of the sheet 2 is nipped and therefore stopped by the registration roller pair 12. The cam member 75 is rotated in synchronism with the print drum 20.

At preselected registration timing, the control unit 50 starts driving the stepping motor 28. Consequently, the registration roller pair 12 starts conveying the sheet 2 toward the printing section 4 between the print drum 20 and the press roller 22. Then, the press roller 22 is brought into contact with the print drum 20 for forming an image on the sheet 2.

More specifically, when the leading edge of the sheet 2 is nipped between the print drum 20 and the press roller 22 at the printing section 4, the cam 75 with the profile stated previously pushes the cam follower arm 81 upward little by little with the result that the shaft 78 rotates clockwise, as viewed in FIG. 4. Consequently, the arm members 73A and 73B affixed to the shaft 78 are also moved in the spacing direction in accordance with the rotation of the cam member 75, releasing the driven roller 12B from the drive roller 12A.

When the driven roller 12B is released from the drive roller 12A, the sheet 2, now free from the resistance of the registration roller pair 12, is conveyed in accordance with the peripheral speed of the print drum 20. Although the pin 85 moves in interlocked relation to the arm members 73A and 73B, the slot 89 absorbs the movement of the pin 85 to thereby prevent the link member 86 from moving in the releasing direction and exerting a load on the release motor 87. The sheet 2, carrying an image transferred thereto from the master 19 at the printing section 4, is driven out to the print tray 25 by the belt conveyor 25, which includes the suction fan 24, FIG. 1, as stated earlier.

When the operation stated above is repeated a number of times corresponding to the desired number of prints input by the operator, the control unit 5O causes the printer to stop operating.

Assume that the jam sensor 27 outputs a jam signal when the printer is in operation. Then, the control unit 50 drives the release motor 87 while interrupting the operation of the other sections of the printer. As shown in FIG. 5, the release motor 87 causes the link member 86 to move in the releasing direction or rightward, as indicated by an arrow, while pulling the pin 85 loosely fitted in the slot 89 in the same direction. Consequently, the shaft 78 is forcibly rotated clockwise without regard to the position of the cam member 75, releasing the roller 80 mounted on the cam follower arm 81 from the cam surface 75 aof the cam member 75. This, in turn, causes the arm members 73A and 73B to turn clockwise against the action of the tension springs 74A and 74B, thereby releasing the driven roller 12B from the drive roller 12A.

As stated above, in the illustrative embodiment, as soon as the jam sensor 27 senses a jam, the printer immediately stops operating and causes the release motor 87 to move the arm members 73A and 73B and cam follower arm 81 in the spacing direction. As a result, the driven roller 12 and drive roller 12A are immediately released from each other without regard to the position of the cam member 75. This prevents the sheet 2 from being conveyed by the drive roller 12A and driven roller 12B pressed against each other in the direction X and therefore prevents the sheet jam from being aggravated, allowing the operator to easily remove a jamming sheet 2.

Moreover, the link member 86 and release motor 87 are interconnected by the gear portion 90 and worm gear 88 held in mesh with each other. It follows that even if the power supply to the release motor 87 is shut off while the operator is dealing with a sheet jam, the arm members 73A and 73B and cam follower arm, 81 are prevented from being returned toward the contact position under the action of the tension springs 74A and 74B. This further promotes easy removal of a jamming sheet 2.

On the other hand, to return the driven roller 12B to the position where it contacts the drive roller 12A, the operator operates the return key switch 62. In response, the control unit 50 causes the release motor 87 to rotate in the direction opposite to the direction in which it rotated in the event of release, so that the link member 86 moves leftward, as viewed in FIG. 5, opposite to the releasing direction (rightward) while entraining the pin 85 received in the slot 89 in the same direction. The pin 85, in turn, causes the shaft 78 to rotate counterclockwise, as viewed in FIG. 5, such that the cam follower arm 81 moves the roller 80 toward the cam surface 75 aof the cam member 75. Consequently, the arms 73A and 73B are angularly moved counterclockwise, as viewed in FIG. 5, under the action of the tension springs 74A and 74B as well, causing the driven roller 12B to contact the drive roller 12B.

Now, it may occur that the stencil printer is left unused over a long time, depending on the user's circumstances. This brings about a problem that if the driven roller 12B is pressed against the drive roller 12A throughout the unused period, then the rollers 12A and 12B are apt to deform due to the force of the tension springs 74A and 74B constantly acting thereon. The illustrative embodiment solves this problem with the following configuration.

The operator of the printer operates the release key switch 61. In response to the resulting release command signal output from the release key switch 61, the control unit 50 drives the release motor 87 to cause the link member 86 to move in the releasing direction, i.e., rightward in FIG. 5 while entraining the pin 86 received in the slot 89 in the same direction. As a result, the shaft 78 is rotated clockwise without regard to the position of the cam member 75, releasing the roller 80 of the cam follower arm 81 from the cam surface 75 aof the cam member 75. This, in turn, causes the arm members 73A and 73B to turn clockwise against the action of the tension springs 74A and 74B, thereby releasing the driven roller 12B from the drive roller 12A.

As stated above, in the illustrative embodiment, the operator may operate the release key switch 61 any time in order to release the driven roller 12B from the drive roller 12A without regard to the position of the cam member 75. This successfully protects the drive roller 12A and driven roller 12B from deformation ascribable to the force of the tension springs 74A and 74B even when the printer is left unused over a long time.

Reference will be made to FIG. 7 for describing a modification of the illustrative embodiment. As shown, in the modification, the drive source of the second moving means 72 is implemented by a solenoid 97 having a plunger 97 ainstead of the release motor 87. As for the rest of the construction, the modification is identical with the illustrative embodiment. The plunger 97 aof the solenoid 97 is pinned to the end 86 bof the link member 86. The solenoid 97 is of the type pulling the plunger 97 awhen energized. If desired, the plunger 97 amay be directly connected to the pin 86 without the intermediary of the link member 86, in which case the slot 89, FIG. 3, will be formed in the plunger 97 a.

FIG. 8 shows a control system included in the above modification. As shown, the solenoid 97 is connected to the output side of a control unit 50A, which is basically identical with the control means 50, FIG. 6, in configuration and function. The difference is that the control unit 50A energizes the solenoid 97 in response to a jam signal output from the jam sensor 27 or a release command signal output from the release key switch 61 and deenergizes the solenoid 97 in response to a return command signal output from the return key switch 62.

When the jam sensor 27 outputs a jam signal during the operation of the printer, the control unit 50A energizes the solenoid 97 while interrupting the operation of the other sections of the printer. As shown in FIG. 7, the solenoid 97 causes the link member 86 to move in the releasing direction or rightward while pulling the pin 85 loosely fitted in the slot 89 in the same direction. Consequently, the shaft 78 is forcibly rotated clockwise without regard to the position of the cam member 75, releasing the roller 80 mounted on the cam follower arm 81 from the cam surface 75 aof the cam member 75. This, in turn, causes the arm members 73A and 73B to turn clockwise against the action of the tension springs 74A and 74B, thereby releasing the driven roller 12B from the drive roller 12A.

As stated above, in the modification, as soon as the jam sensor 27 senses a jam, the printer immediately stops operating and causes the solenoid 97 to move the arm members 73A and 73B and cam follower arm 81 in the spacing direction. As a result, the driven roller 12 and drive roller 12A are immediately released from each other without regard to the position of the cam member 75. This prevents the sheet 2 from being conveyed by the drive roller 12A and driven roller 12B pressed against each other in the direction X and therefore prevents the sheet jam from being aggravated, allowing the operator to easily remove a jamming sheet 2.

Again, to return the driven roller 12B to the position where it contacts the drive roller 12A, the operator operates the return key switch 62. In response, the control unit 50 deenergizes the solenoid 97. As a result, the force of the tension springs 74A and 74B and the total weight of the arms and rollers act on the link member 86 and cause it to move leftward, as viewed in FIG. 7, inverse to the releasing direction (rightward) while entraining the pin 85 received in the slot 89 in the same direction. The pin 85, in turn, causes the shaft 78 to rotate counterclockwise such that the cam follower arm 81 moves the roller 80 toward the cam surface 75 aof the cam member 75. Consequently, the arms 73A and 73B are angularly moved counterclockwise under the action of the tension springs 74A and 74B as well, causing the driven roller 12B to contact the drive roller 12B. The operator is allowed to operate the release key switch 61 any time in order to release the driven roller 12B from the drive roller 12A, as desired.

In the illustrative embodiment and modification thereof described above, the releasing device 70 is applied to the registration roller pair 12 by way of example. However, the releasing device 70 is similarly applicable to any other conveying members that cooperate to convey the sheet 2 while nipping it therebetween. Also, conveying members to which the releasing device 70 is applicable are not limited to a pair of rollers. For example, a pair of rollers may be replaced with the combination of a drive belt member and a driven roller member contacting or preferably pressed against the belt member or the combination of a drive belt member and a driven belt member contacting or pressed against each other. If desired, the cooperative conveying members may even be replaced with members neither one of which is driven or both of which are driven.

It should be noted that the stencil printer including the releasing means 70 shown and described is merely an example of a printer. Further, the printer may be replaced with any other image forming apparatus, e.g., a conventional electrophotographic image forming apparatus in which an image transfer station is formed between a photoconductive element or image carrier, which is implemented as a drum or a belt on which a toner image is to be formed, and an image transfer member implemented as a roller or a belt and configured to transfer the toner image to a sheet.

In summary, it will be seen that the present invention provides a releasing device capable of allowing a jamming sheet to be easily removed with first moving means for moving one of two conveying members into or out of contact with the other conveying member and second moving means connected to the first moving means for moving the one conveying member away from the other conveying member independently of the first moving means.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof. 

1. A releasing device for a pair of conveying members one of which is selectively movable into or out of contact with the other, said pair of conveying members being capable of conveying a sheet while nipping said sheet therebetween, said releasing device comprising: first moving means for selectively moving one of the pair of conveying members into or out of contact with the other conveying member; and second moving means for moving the one conveying member away from the other conveying member independently of an operation of said first moving means.
 2. The releasing device as claimed in claim 1, wherein said first moving means comprises an angularly movable member supporting the one conveying member, means for constantly biasing said angularly movable member in a contacting direction, and a rotatable cam member engaged with said angularly movable member for causing said angularly movable member to selectively move in said contacting direction or a spacing direction.
 3. The releasing device as claimed in claim 2, wherein said second moving means comprises a link member connected to said angularly movable member at one end and a drive source connected to the other end of said link member for moving said link member in a releasing direction in which said angularly movable member moves in the spacing direction.
 4. The releasing device as claimed in claim 3, further comprising control means for driving said drive source on receiving a jam signal representative of a sheet jam.
 5. The releasing device as claimed in claim 4, further comprising release commanding means for outputting a release command signal and control means for driving said drive source on receiving said release command signal.
 6. The releasing device as claimed in claim 5, further comprising return commanding means for outputting a return command signal, said control means driving, on receiving said return command signal, said drive source in an opposite direction.
 7. The releasing device as claimed in claim 5, wherein said drive source comprises a solenoid, said releasing means further comprises return commanding means for outputting a return command signal, and said control means deenergizes said solenoid on receiving said return command signal from said return commanding means.
 8. An image forming apparatus comprising: an image transferring section; and a pair of conveying members one of which is selectively movable into or out of contact with the other, said pair of conveying members being capable of conveying a sheet while nipping said sheet therebetween; and releasing means for releasing the one conveying member from the other conveying member; said releasing means comprising: first moving means for selectively moving the one conveying member into or out of contact with the other conveying member; second moving means for moving the one conveying member away from the other conveying member independently of an operation of said first moving means.
 9. The apparatus as claimed in claim 8, wherein said image transferring section comprises a print drum around which a master formed with an image is to be wrapped and a pressing member configured to nip the sheet between said pressing member and said print drum. 